Method for bending metal sheet and device for regulating residual stress

Abstract

A method for bending a flat workpiece is provided. The method may include applying heat or pressure to the workpiece at a range within a first width from an edge with a residual stress formed by cutting so as to reduce the residual stress, and bending the workpiece along a bending line after applying the heat or pressure.

1 . A method for bending a flat workpiece, the method comprising:
 applying heat or pressure to the workpiece at a range within a first width from an edge with a residual stress formed by cutting so as to reduce the residual stress; and   bending the workpiece along a bending line after applying the heat or pressure.   
     
     
         2 . The method of  claim 1 , wherein the range is limited in a band running in parallel with but not including the bending line. 
     
     
         3 . The method of  claim 1 , wherein the first width is longer than 0.1 mm and shorter than 10 mm. 
     
     
         4 . The method of  claim 1 , further comprising:
 calculating a first bending moment (Mrs) in a ridge line originated from the residual stress, and a second bending moment (Mz) in the ridge line originated from bending to obtain a total bending moment (Mrs−Mz);   calculating a camber curvature (ρz) of the workpiece originated from the total bending moment (Mrs−Mz); and   regulating an amount of the heat or intensity of the pressure so as to make a difference between the camber curvature (ρz) and a target value (ρz 0 ) be equal to or less than a tolerable range.